Distributed identity-based firewalls

ABSTRACT

Systems and techniques are described for monitoring network communications using a distributed firewall. One of the techniques includes receiving, at a driver executing in a guest operating system of a virtual machine, a request to open a network connection from a process associated with a user, wherein the driver performs operations comprising: obtaining identity information for the user; providing the identity information and data identifying the network connection to an identity module external to the driver; and receiving, by a distributed firewall, data associating the identity information with the data identifying the network connection from the identity module, wherein the distributed firewall performs operations comprising: receiving an outgoing packet from the virtual machine; determining that the identity information corresponds to the outgoing packet; and evaluating one or more routing rules based at least in part on the identity information.

BACKGROUND

This document relates to monitoring virtual machine network communications.

A virtual machine is a software-based abstraction of a physical computer system. In general, a computer program that can be executed on a physical computer system can be executed in a virtual machine using virtualization software. Virtualization software is software that is logically interposed and interfaces with a virtual machine and a physical computer system. Each virtual machine is configured to execute an operating system, referred to herein as a guest OS, and applications. A physical computer system, referred to herein as a host machine or physical machine, can execute one or more virtual machines.

SUMMARY

In general, one aspect of the subject matter described in this document can be embodied in a technique that includes receiving, at a driver executing in a guest operating system of a virtual machine, a request to open a network connection from a process associated with a user, wherein the driver performs operations comprising: obtaining identity information for the user; providing the identity information and data identifying the network connection to an identity module external to the driver; and receiving, by a distributed firewall, data associating the identity information with the data identifying the network connection from the identity module, wherein the distributed firewall performs operations comprising: receiving an outgoing packet from the virtual machine; determining that the identity information corresponds to the outgoing packet based on a comparison between source information for the outgoing packet and the data received from the identity module; and evaluating one or more routing rules based at least in part on the identity information. Other embodiments of this aspect include corresponding systems, apparatus, and computer software encoded on a non-transitory machine readable storage medium.

These and other aspects can optionally include one or more of the following features. The operations performed by the distributed firewall can further include: forwarding the outgoing packet when approved according to the routing rules. The operations performed by the distributed firewall can further include: blocking the packet when denied according to the routing rules.

The distributed firewall can be implemented in a hypervisor that is configured to monitor the virtual machine. The identity information can be a security identifier (SID) for the user. Evaluating the one or more routing rules can further include: evaluating the one or more routing rules based in part on one or more of a source Internet Protocol (IP) address for the outgoing packet, a source port number for the outgoing packet, an intended destination IP address for the outgoing packet, or an intended destination port number for the outgoing packet.

The technique can further include receiving, by the identity module, the identity information and the data identifying the network connection; generating, by the identity module, data associating the identity information with the data identifying the network connection; and providing, by the identity module, the data associating the identity information with the data identifying the network connection to the distributed firewall. The data identifying the network connection can include an Internet Protocol (IP) address and one or more port numbers assigned to the network connection.

In general, another aspect of the subject matter described in this document can be embodied in a technique that includes receiving, at a driver executing in a guest operating system of a virtual machine, a request to open a network connection from a process associated with a user, wherein the driver performs operations comprising: obtaining identity information for the user; receiving an outgoing packet from the process over the network connection; adding the identity information for the user to the outgoing packet to generate a second packet; and providing the second packet to a first system external to the network driver; and receiving, by the first system, the second packet from the driver, wherein the first system performs operations comprising: evaluating one or more routing rules based at least in part on the identity information of the second packet. Other embodiments of this aspect include corresponding systems, apparatus, and computer software encoded on a non-transitory machine readable storage medium.

These and other aspects can optionally include one or more of the following features. The operations performed by the first system can further include: forwarding the second packet when approved according to the routing rules, wherein the forwarded second packet does not include the identity information. The operations performed by the first system can further include: blocking the second packet when denied according to the routing rules. The first system can be implemented in a hypervisor that is configured to monitor the virtual machine.

Forwarding the second packet can include: modifying the second packet by removing the identity information from the second packet; and forwarding the modified second packet to a virtual switch implemented in the hypervisor for transmission to an intended recipient of the outgoing packet. The identity information can be a security identifier (SID) for the user. Evaluating the one or more routing rules can further include: evaluating the one or more routing rules based in part on one or more of a source internet protocol (IP) address for the second packet, a source port number for the second packet, an intended destination IP address for the second packet, or an intended destination port number for the second packet.

Particular embodiments of the subject matter described in this document can be implemented so as to realize one or more of the following advantages. Accurate identity information or users of virtual machines can be provided to a firewall for use in implementing identity-based routing rules. Identity-based routing rules can be effectively used with low latency and without limiting performance of the virtual machine or the physical machine hosting the virtual machine. By executing a respective identity-based firewall module for each virtual machine in the hypervisor of the physical machine hosting the virtual machine, identity-based routing rules can be effectively implemented in a distributed and scalable manner. Identity-based routing rules can be accurately applied to communications received from multi-user virtual machines, e.g., from Virtual Desktop Infrastructure (VDI) virtual machines that experience frequent log ins and log outs from multiple users or from terminal servers having multiple users logged in at the same time.

The details of one or more embodiments of the subject matter described in this document are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an architecture for an example system that is configured to monitor virtual machine network traffic using a distributed firewall.

FIG. 1B shows an architecture for an example system that is configured to provide identity information to a distributed firewall using an identity module.

FIG. 2 shows example identity-based routing rules.

FIG. 3 is a flowchart of an example technique for processing an outgoing packet using a distributed identity-based firewall as implemented on one or more data processing apparatus.

FIG. 4 is a flowchart of another example technique for processing an outgoing packet using a distributed identity-based firewall as implemented on one or more data processing apparatus.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

This specification generally describes techniques for implementing a hypervisor-based firewall that can apply routing rules to outgoing communications from virtual machines. The routing rules are based at least in part on the identity of the user associated with the process initiating the outgoing communication.

FIG. 1A shows an architecture for an example system 100 that is configured to monitor virtual machine (VM) network communications using a distributed firewall. In the system 100, a physical machine 102 is configured to execute VMs 150 a through 150 c using a hypervisor 106. The physical machine 102 is one or more data processing apparatus that each includes a hardware platform 104. The hardware platform 104 may include, e.g., a local storage device, a network adapter, memory, a processor, and so on.

The hypervisor 106 is a virtualization software layer that executes on the hardware platform 104. The hypervisor 106 manages a virtual machine execution space 108 within which one or more VMs, e.g., VMs 150 a-150 c, may be concurrently instantiated and executed. For each of the VMs 150 a-150 c, the hypervisor 106 manages a corresponding virtual hardware platform. Each virtual hardware platform includes emulated hardware, e.g., a virtual storage device, a virtual network adapter/interface, virtual memory, a virtual processor, and so on.

Each virtual machine managed by the hypervisor 106 executes a guest operating system, e.g., guest operating system 152 a, that executes user applications, e.g., user applications 154 c. The hypervisor 106 transforms input/output (I/O) requests from the guest operating systems to the corresponding virtual hardware platform into corresponding requests to the hardware platform 104.

The hypervisor 106 includes a respective distributed firewall module, e.g., distributed firewall modules 160 a-160 c, for each virtual machine managed by the hypervisor 106. Each distributed firewall module receives outgoing communications, e.g., packets intended for transmission to other virtual machines executing on the physical machine 102 or for transmission to a different physical machine over a network, sent by the corresponding virtual machine and determines whether to allow, block, redirect or take some other action with respect to each communication in accordance with a respective set of routing rules. While FIG. 1 shows a respective distributed firewall module for each virtual machine managed by the hypervisor, in some implementations, one or more of the distributed firewall modules 160 c-160 c can be assigned to manage communications for multiple virtual machines managed by the hypervisor 106.

Advantageously, the routing rules can include identity-based rules, i.e., rules that determine what action should be taken with respect to a communication based in part on the identity or the group membership of the user that is sending the communication. Example identity-based routing rules will be described in more detail below with reference to FIG. 2. Once a distributed firewall module, e.g., one of the distributed firewall modules 160 a-160 c, has determined to allow a communication to be transmitted, the distributed firewall module forwards the communication to a virtual switch 120 in the hypervisor 106 for distribution to the determined destination, e.g., using a network adaptor in the hardware platform 104 of the physical machine 102. The virtual switch 120 is an emulated hardware switch that executes in the hypervisor 120 and routes network communications between VMs executing on the physical machine 102 or to and from external data processing apparatus using the network adaptor in the hardware platform 104. The identity-based rules can optionally also be applied to incoming communications, i.e., the distributed firewall modules can determine what action should be taken with respect to a communication received from the virtual switch 120 and intended for one of the VMs 150 a-150 c based in part on the identity or the group membership of the user that is the intended recipient of the communication.

In order to provide the distributed firewall module 160 a with identity information for any given outgoing communication sent by, e.g., one of the user applications 154 c of the VM 150 a, a network driver 156 a executes in the guest operating system 152 a of VM 150 a. The network driver 156 a is a protocol stack that implements a computer networking protocol suite such as, for example, Transmission Control Protocol/Internet Protocol (TCP/IP). In some implementations, the network driver 156 a implements the Transport Driver Interface (TDI). Other protocol suites are possible. The protocol stack comprises modules or layers that each implement a portion of the protocol suite and can communicate with each other. In some implementations, the network driver implements some or all of the Open Systems Interconnection (OSI) model layers. In some implementations, the network driver 156 a executes entirely or partially in the kernel space of the guest OS 152 a. In other implementations, the network driver 156 a executes in the user space of the guest OS 152 a. Kernel space is a protected memory area generally reserved for running the guest OS 152 a kernel, kernel extensions, and device drivers. User space is a memory area where user mode applications execute. In some implementations, the network driver 156 a communicates with the hypervisor 106 through a network adaptor or interface in the emulated hardware.

The network driver 156 a detects network events. In some implementations, the network driver 156 a can also deny or modify outgoing packets before they are transmitted to the distributed firewall module 160 a. When a request is received from one of the user applications 154 c or from another process executing on the VM 150 a to open a network connection, the network driver 156 a obtains identity information for the user associated with the process. The identity information is used by the distributed firewall module 160 a to determine what action to take with respect to each packet that is transmitted over the network connection. For example, the identity information may be a Security Identifier (SID) or other identifier of a user currently logged in to the virtual machine, e.g., a username of the user or group membership information for the user.

In some implementations, the network driver 156 a adds the obtained identity information into an outgoing packet and transmits the outgoing packet to the distributed firewall module 160 a. An example technique for processing packets that are transmitted over a network connection using identity information that has been added to an outgoing packet is described below with reference to FIG. 3. In some other implementations, the network driver 156 a transmits the obtained identity information to an identity module.

FIG. 1B shows an architecture for an example system 150 that is configured to provide identity information to a distributed firewall using an identity module. In the system 150, the network driver 156 a and the distributed firewall module 160 a can communicate with an identity module 170. The identity module 170 can be executed by the physical machine 104 as part of the hypervisor 106 or the VM execution space 108. Alternatively, the identity module 170 can execute on an external data processing apparatus, i.e., on a separate physical machine from the network driver 156 a and the distributed firewall module 160 a.

The identity module 170 receives identity information and network connection information from the network driver 156 a and provides data associating the network connection with the identity information to the distributed firewall 160 a for use in determining what action to take with respect to packets that are transmitted over the network connection. An example technique for processing packets that are transmitted over a network connection using identity information received from an identity module is described below with reference to FIG. 4.

FIG. 2 shows example identity-based routing rules. The identity-based routing rules can be used by a distributed firewall module, e.g., one of the distributed firewall modules 160 a of FIG. 1, to determine an appropriate action in response to receiving an outgoing packet from a VM. Each identity-based routing rule specifies criteria for an outgoing packet and an action to be taken when the outgoing packet satisfies the criteria. For example, identity-based routing rule 202 specifies originating criteria, i.e., that the outgoing packet must originate from a user in a security group “SecGrp1” and from a port “port1,” destination criteria, i.e., that the outgoing packet must be intended for a destination IP address “Dst IP” and a destination port “port,” and an action “action1” to be taken by the distributed firewall module when the outgoing packet satisfies the criteria. The action may be, e.g., to allow the packet to proceed to the intended destination, to re-direct the packet to a different destination, to block the packet from being transmitted, and so on. Other types of routing rules with or without qualifiers, e.g., log, copy, and so on, are possible.

As another example, identity-based routing rule 204 specifies that, for a packet originating from a user in a user group “SecGrp2” and from a port “port2,” and intended for the same destination IP address “Dst IP” and destination port “port,” a different action “action2” should be taken by the distributed firewall module. While rules 202 and 204 are examples of identity-based rules in which packet routing depends on the user group membership of a user sending the packet, other identity-based rules are possible in which packet routing is different for each different user, i.e., is based on a unique identifier of a user sending the packet. Additionally, while the rules 202 and 204 specify group-based routing criteria, the identity information received by the distributed firewall module may include a user identifier, e.g., a security identifier (SID) for the user. In these cases, the distributed firewall module may need to store data identifying the members of user groups included in routing rules. For example, the distributed firewall may store data 206 indicating that the members of the group “SecGrp1” are the users having identifiers “ID1,” “ID2” and “ID3.” As another example, the distributed firewall may store data 208 indicating that the members of the group “SecGrp2” are the users having identifiers “ID4,” “ID5,” and “ID6.”

In some implementations, e.g., in implementations that make use of the technique described below with reference to FIG. 4, it may be necessary for the distributed firewall module to determine identity information from the sender information of an outgoing packet. That is, the distributed firewall module may obtain and store data that associates a source IP address and port number with a user identifier or user group identifier. For example, the distributed firewall may store data 210 that indicates that packets received from source IP address “Src IP1” and port “port1” are associated with a user identified by the identifier “ID1.” As another example, data 212 identifies an association between a source IP address “Src IP3” and a user identified by the identifier “ID5.” Each piece of association data may be stored with an indication of whether or not the association is temporary or permanent. A temporary association is an association that is only valid while a network connection is open and expires when the network connection is closed. A permanent association is an association that is valid independent of the network connection used to transmit the outgoing packet. For example, the data 210 identifies the association as temporary while the data 212 identifies the association as temporary.

FIG. 3 is a flowchart of an example technique 300 for processing an outgoing packet using a distributed identity-based firewall as implemented on one or more data processing apparatus.

At step 302, a network driver, e.g., the network driver 150 a of FIG. 1, executing as part of a guest operating system of a VM, e.g., the guest operating system 152 a of the VM 150 a of FIG. 1, receives a request to open a network connection from a user process executing on the VM. For example, the process can be a user application, e.g., one of the user applications 154 c of FIG. 1.

At step 304, the network driver determines identity information for a user associated with the process. For example, the network driver can determine the SID for the user currently logged into the VM. The system can obtain the identity information from the guest operating system by, e.g., submitting a request for the information to the operating system using an Application Programming Interface (API) provided by the guest operating system. While the identification information is being determined, the network driver blocks the requested network connection, i.e., prevents any packets from being transmitted using the connection.

At step 306, the network driver receives an outgoing packet to be transmitted over the network connection.

At step 308, the network driver adds the determined identity information to the outgoing packet. The network driver can use any of a variety of techniques to add the identity information to the packet. For example, a tunnel may be established between the network driver and a distributed firewall module for the VM, e.g., the distributed firewall module 160 a of FIG. 1. The tunnel may be established using any of a variety of tunneling protocols, e.g., Generic Routing Encapsulation (GRE), NVGRE (Network Virtualization using Generic Routing Encapsulation), and so on. The network driver can then encapsulate the outgoing packet into a tunneling packet and insert the identity information into the header of the tunneling packet.

At step 310, the network driver transmits the packet to the distributed firewall module for the VM. For example, the system can transmit the tunneling packet that includes the encapsulated outgoing packet to the distributed firewall module in accordance with the tunneling protocol.

At step 312, the distributed firewall module receives the outgoing packet with the identity information. For example, the distributed firewall module may receive the tunneling packet and extract the outgoing packet and the identity information from the tunneling packet.

At step 314, the distributed firewall module determines whether to allow or block the outgoing packet. The distributed firewall module can make the decision by evaluating the identity information, other information about the source, e.g., the source IP address, port number, or both, and information about the destination of the intended destination of the packet, e.g., the destination IP address, port number, or both, against a set of identity-based rules as described above with reference to FIG. 2.

At step 316, if the packet is allowed, the distributed firewall module removes the identity information added by the network driver to the packet and forwards the packet to a virtual switch, e.g., the virtual switch 120 of FIG. 1, for transmission to the intended recipient. Alternatively, if the routing rule indicates that the packet should be redirected to a different destination, the distributed firewall module removes the identity information and forwards the packet to the virtual switch for transmission to the intended recipient.

At step 318, if the packet is blocked, the distributed firewall system removes the identity information added by the network driver to the packet but prevents the packet form being sent to the intended recipient.

In some implementations, once a network connection has been opened, the network driver continues using the determined identity information for the connection until the network connection is closed, i.e., until the network driver receives an indication from the VM that a disconnect for the network connection has occurred or until a timer associated with the connection expires. In some other implementations, if the network driver receives updated identity information that indicates a change in the identity information of the user associated with the process while a network connection is open, the network connection may close or drop the open network connection.

As described with reference to the technique 300, a network driver executing on the VM modifies each outgoing packet to include user identity information. However, in some circumstances, it may not be possible or advantageous for the driver or another process executing on the VM to modify outgoing packets.

FIG. 4 shows a flowchart for another example technique 400 for processing an outgoing packet using a distributed identity-based firewall as implemented on one or more data processing apparatus.

At step 402, a network driver, e.g., the network driver 150 a of FIG. 1, executing as part of a guest operating system of a VM, e.g., the guest operating system 152 a of the VM 150 a of FIG. 1, receives a request to open a network connection from a user process executing on the VM. For example, the process can be a user application, e.g., one of the user applications 154 c of FIG. 1.

At step 404, the network driver determines identity information for a user associated with the process. While the identification information is being determined, the network driver blocks the requested network connection, i.e., prevents any packets from being transmitted using the connection.

At step 406, the network driver transmits the determined identity information and information identifying the requested network connection to an identity module. The identity module can be, e.g., a process executing on the same physical machine as the VM, e.g., the physical machine 102, or on an external data processing apparatus. The information identifying the requested network connection can be, e.g., the IP address of the VM and the port or ports allocated to the network connection. The identity module is responsible for receiving requests from the network driver and transmitting data associating data identifying a network connection with data identifying the user of the process that establishes the network connection to a distributed firewall module corresponding to the VM, e.g., the distributed firewall module 160 a of FIG. 1. For example, the data can associate a source VM and one or more port numbers with a SID. Additionally, the data transmitted by the identity module to the distributed firewall module can identify the transmitted data as temporary, i.e., only for use while the network connection is open. Temporary data can be used, e.g., until a timer associated with the data expires or until an indication is received from the VM that a disconnect for the network connection has occurred.

At step 408, the distributed firewall module receives the data associating the network connection with the identity information from the identity module. The distributed firewall module stores the received data with an indication of whether the received data is temporary or permanent.

At step 410, the distributed firewall module receives an outgoing packet from the VM.

At step 412, the distributed firewall module determines identity information for the packet. For example, the distributed firewall module can compare the source information for the packet, e.g., the source IP address and source port for the packet, to the data received from the identity module to identify a corresponding user identifier. That is, the distributed firewall module can determine which identity information corresponds to the outgoing packet by accessing data previously received from the identity module.

At step 414, the distributed firewall module determines whether to allow or block the outgoing packet. The distributed firewall module can make the decision by evaluating the identity information, other information about the source, e.g., the source IP address, port number, or both, and information about the destination of the intended destination of the packet, e.g., the destination IP address, port number, or both, against a set of identity-based rules as described above with reference to FIG. 2.

At step 416, if the packet is allowed, the distributed firewall module forwards the packet to a virtual switch, e.g., the virtual switch 120 of FIG. 1, for transmission to the intended recipient. Alternatively, if the routing rule indicates that the packet should be redirected to a different destination, the distributed firewall module forwards the packet to the virtual switch for transmission to the intended recipient.

At step 418, if the packet is blocked, the distributed firewall system prevents the packet from being sent to the intended recipient.

Embodiments of the subject matter and the operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this document can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

The operations described in this document can be implemented as operations performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources. The term “data processing apparatus” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations, of the foregoing. The apparatus can include special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform actions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, embodiments of the subject matter described in this document can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user's client device in response to requests received from the web browser.

Embodiments of the subject matter described in this document can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described in this document, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), an inter-network (e.g., the Internet), and peer-to-peer networks (e.g., ad hoc peer-to-peer networks).

The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. In some embodiments, a server transmits data (e.g., an HTML page) to a client device (e.g., for purposes of displaying data to and receiving user input from a user interacting with the client device). Data generated at the client device (e.g., a result of the user interaction) can be received from the client device at the server.

While this document contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous. 

What is claimed is:
 1. A computer-implemented method comprising: receiving, at a driver executing in a guest operating system of a virtual machine (VM) operating on a physical host machine, a request to open a network connection from a process associated with a user, wherein the driver performs operations comprising: obtaining identity information for the user from the guest operating system of the VM, wherein the driver prevents transmission of any packets for the network connection until the identity information is obtained; and providing the identity information and data identifying the network connection to an identity module external to the driver and operating within virtualization software of the physical host machine; and at a firewall for the VM that operates within the virtualization software of the physical host machine: receiving, from the identity module, data associating source information for an outgoing packet from the VM with an identifier associated with one or more firewall rules, the identifier based on the identity information provided to the identity module by the driver; determining that the outgoing packet matches the associating data received from the identity module, based on a comparison between source information for the outgoing packet and source information in the associating data received from the identity module; and based at least in part on the identifier in the associating data received from the identity module, evaluating one or more firewall rules to identify a firewall rule that is applicable to the outgoing packet, said evaluating comprising comparing a set of header values of the outgoing packet with a set of packet-matching values of an evaluated firewall rule.
 2. The method of claim 1 further comprising forwarding the outgoing packet when approved according to the firewall rules.
 3. The method of claim 1 further comprising blocking the packet when denied according to the firewall rules.
 4. The method of claim 1, wherein the firewall is a distributed firewall configured to monitor the VM, wherein additional distributed firewalls operate within the virtualization software, each additional distributed firewall configured to monitor a different additional VM operating on the physical host machine.
 5. The method of claim 1, wherein the identity information is a security identifier (SID) for the user.
 6. The method of claim 1, further comprising: at the identity module operating on the physical host machine: receiving the identity information and the data identifying the network connection; generating the data associating source information for outgoing packets from the VM with the identifier associated with one or more firewall rules; and providing the generated data to the firewall.
 7. The method of claim 1, wherein the data identifying the network connection comprises an Internet Protocol (IP) address and one or more port numbers assigned to the network connection.
 8. The method of claim 2, wherein forwarding the outgoing packet further comprises forwarding the packet to a virtual switch executing within the virtualization software for distribution to a destination of the packet.
 9. The method of claim 1 further comprising storing, at the firewall, the received data associating source information with the identifier with an indication of whether the association between the source information and the identifier is temporary or permanent.
 10. The method of claim 1, wherein the driver is further configured to deny and modify outgoing packets before the outgoing packets are transmitted to the firewall.
 11. The method of claim 1, wherein the user is a user currently logged into the VM.
 12. The method of claim 1 further comprising redirecting the outgoing packet to a different destination according to the firewall rules.
 13. A computer comprising: one or more processing units; and one or more non-transitory machine-readable storage devices storing: a first set of instructions, for a driver executing in a guest operating system of a virtual machine (VM) operating on the computer, that when executed by the one or more processing units causes the one or more processing units to perform operations comprising: receiving, at the driver, a request to open a network connection from a process associated with a user: obtaining identity information for the user from the guest operating system of the VM, wherein the driver prevents transmission of any packets for the network connection until the identity information is obtained; and providing the identity information and data identifying the network connection to an identity module external to the driver and executing within virtualization software of the computer; and a second set of instructions, for a distributed firewall for the VM that operates within the virtualization software of the computer, that when executed by the one or more processing units causes the one or more processing units to perform operations comprising: receiving, from the identity module, data associating source information for an outgoing packet from the VM with an identifier associated with one or more firewall rules, the identifier based on the identity information provided to the identity module by the driver; determining that the outgoing packet matches the associating data received from the identity module, based on a comparison between source information for theoutgoing packet and the source information in the associating data received from the identity module; and based at least in part on the identifier in the associating data received from the identity module, evaluating one or more firewall rules to identify a firewall rule that is applicable to the outgoing packet, said evaluating comprising comparing a set of header values of the outgoing packet with a set of packet-matching values of an evaluated firewall rule.
 14. The computer of claim 13, wherein the second set of instructions further cause the one or more processing units to forward the outgoing packet when approved according to the firewall rules.
 15. The computer of claim 13, wherein the second set of instructions further cause the one or more processing units to block the packet when denied according to the firewall rules.
 16. The computer of claim 13, wherein the distributed firewall is configured to monitor the VM, wherein additional distributed firewalls operate within the virtualization software, each additional distributed firewall configured to monitor a different additional VM operating on the computer.
 17. The computer of claim 13, wherein the identity information is a security identifier (SID) for the user.
 18. The computer of claim 13, wherein the data identifying the network connection comprises an Internet Protocol (IP) address and one or more port numbers assigned to the network connection. 